Royal Garden in Waikiki was very adult oriented. Location and mostly studio units makes this very much a couples resort. Not by the beach, so 6 block walk to the centre of things, but it is in a much quieter part of Waikiki.
Agree, La Belle Maison is generally very adult. Similar situation at Canterbury in San Francisco.
When we last visited Flagstaff on Canada's Victoria Day weekend (a week earlier than Memorial Day) it was very quiet and very adult, cheap off season points then too. Have not stayed there but Sedona is likely very adult oriented, and more a resort.
When we visited Indio (very much a resort complete with 36 holes of golf) last November which was off season, there were young kids still present at the main pool and lazy river. However, at the second pool there was all of 6 adults with the pool to ourselves one afternoon.
Last February at San Antonio Riverside, and Austin we did not encounter any children. Probably different in summer.
Grand Desert in Vegas is generally very adult, depending on the season (ie when the pool is fully open), but even then one pool is adult only.